Registration Dossier
Registration Dossier
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EC number: 214-685-0 | CAS number: 1185-55-3
Endpoint summary
Administrative data
Description of key information
Trimethoxy(methyl)silane (CAS 1185-55-3, EC No. 214-685-0) is a liquid at standard temperature and pressure, with a measured melting point of <-77°C at 1013 hPa and a measured boiling point of 102°C at 1013 hPa. It has a predicted density of 0.95 g/cm3 at 20°C, a predicted kinematic viscosity of 0.5 mm2/s at 20°C and a measured vapour pressure of approximately 3000 Pa at 20°C and 15000 Pa at 50°C.
The substance is classified for flammability according to Regulation (EC) No. 1272/2008 on the basis of a measured flash point of 7.7°C at 1013 hPa and a measured boiling point of 102°C at 1013 hPa. It has a measured auto-ignition temperature of 238°C at 1013 hPa and is not explosive and not oxidising on the basis of chemical structure.
In contact with water trimethoxy(methyl)silane reacts rapidly (half-life of 2.2 hours at pH 7, <0.033 hours at pH 4, 0.11 hours at pH 9 and 25°C) to produce methylsilanetriol (CAS 2445-53-6, EC No. 219-489-9) and methanol (CAS 67-56-1, EC No. 200-659-6) according to the following equation:
CH3Si(OCH3)3 + 3H2O → CH3Si(OH)3 + 3CH3OH
Therefore, requirements for testing of water-based physicochemical properties for the substance are waived on the basis of instability in water. The properties of the silanol hydrolysis product, methylsilanetriol and methanol are assessed instead.
However, the key physicochemical properties of the submission substance has been predicted. The substance has a predicted log Kow of 0.7 at 20°C and predicted water solubility of 9.1E+04 mg/L at 20°C.
Methanol is miscible with water, has low log Kow (-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C) (OECD 2004a).
The saturation concentration in water of the silanol hydrolysis product, methylsilanetriol is limited by condensation reactions that can occur over time at loadings above approximately 1000 mg/L. However, it is very hydrophilic (calculated solubility is 1.0E+06 mg/L at 20°C using a QSAR method) and has a low log Kow (-2.4, predicted).
It is not expected to be surface active and is not expected to undergo significant dissociation within the environmentally-relevant range. The first dissociation constant of a structurally analogous silanetriol (phenylsilanetriol) has been reported to be around pKa of 10. It is much less volatile than the parent substance with a predicted vapour pressure of 0.053 Pa at 25°C).
Reference:
OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18 - 20 October 2004, Methanol, CAS 67-56-1.
Additional information
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